Home Run Hitting in Statcast Era

Introduction

• There has been remarkable changes in home run hitting during the Statcast period 2015-2025

• Why? What variables influence home runs?

• We will focus on two reasons – batter behavior and ball construction

Data

• Focus on the balls in play

• I have data on all balls in play for all Statcast seasons

• In-Play home run rate is

\[ HR \,\, Rate = 100 \times \left(\frac{HR}{BIP}\right) \]

Balls in Play (BIP) and Home Runs (HR) by Season:

In-Play Home Run Rates

Process of Hitting Home Run

1. Hit the ball well – hard and at the right angle

2. Given that the ball is hit well, the ball has to leave the park

In other words, want high exit velocity with a suitable launch angle.

What is a Launch Angle?

Launch Angle measures the vertical angle, in degrees, at which the ball leaves a player’s bat after being hit.

• Ground ball: Lower than 10 degrees
• Line drive: 10-25 degrees
• Fly ball: 25-50 degrees
• Pop up: Higher than 50 degrees

What is Exit Velocity?

• Exit Velocity measures the speed of the baseball as it comes off the bat, immediately after a batter makes contact.

• Attaining a high Exit Velocity is one of a hitter’s primary goals. A hard-hit ball won’t always have a positive result, but the defense has less time to react, so the batter’s chances of reaching base are higher.

Collect Launch Angle and Exit Velocity for all home runs

Focus on Two Rates

• Red Rate - the rate of balls in play in the RED region

• HR Rate - among the balls in the RED region, what is the home runs rate

• The Red Rate tells us about player behavior, the HR Rate tells us about the ball (its carry properties)

HR Rate is Product of Two Rates

\[ \begin{align} HR \, Rate &= \frac{HR}{BIP} \\ \\ &= \frac{RED}{BIP} \times \frac{HR}{RED} \\ \\ &= P(RED) \times P(HR | RED) \end{align} \]

• \(P(RED)\) measures batter behavior

• \(P(HR | RED)\) measures ball properties

Add RED and HR_RED to Table

In-Play Red Rates Over Statcast Era

What have we learned?

• Players are getting bigger and stronger
• They work on hitting balls with “HR friendly” launch angles
• There has been a steady increase in RED rates

Home Run Rates in Red Region

What have we learned?

• The increase on home run rates depends on more than the players
• The changes in the RED HR rates reflects properties of the ball
• Some seasons, the ball is lively
• In recent seasons, the ball has been relatively dead

This impacts Home Run Records

• Aaron Judge set the AL single season HR record with 62 in the 2022 season

• But 2022 was a “dead-ball” season

• How many home runs would Judge hit with the same exit velocity and launch measurements in 2019?

Does Major League Baseball Care?

• During the big increase in HR hitting, MLB created a committee to study the issue
• Committee made some recommendations
• I don’t think home run hitting is one of the big issues currently